Buy nothing critical / expensive from AliExpress. It's the wild east and chances are you will get screwed. Alibaba yes (if the seller is well known/trusted to you).
Your use case is confusing.
If a battery is for back up and not going to be cycled, then I'm not sure lithium is the right chemistry. It's a lot of money to do no work and you do not want to be keeping lithium at a high state of charge for long periods.
If the battery is going to be cycled, frankly I think you are better to buy a ready made battery from a known reputable manufacturer. It just ends all the second guessing and will be safer.
Do you have any feedback on my questions above, in particular why ready made chinese packs are so much more expensive bought assembled?Not really, prices are not really all that different here.
I’m currently looking to add some limited battery storage capacity to my solar system and looking for some thoughts / sugestions.As @wattmatters said, bit confused about your intended usage. You mention battery and charger, but no mention of either and independent inverter for the batteries or a hybrid inverter? Can you explain a bit more?
As @wattmatters said, bit confused about your intended usage. You mention battery and charger, but no mention of either and independent inverter for the batteries or a hybrid inverter? Can you explain a bit more?
DIY or pre-built will largely depend on your skills and interests.
Take a look at Fogstar as you are in the UK - they have both 5.1kWh and 15kWh prebuild battery packs, sell raw cells and also sell Seplos Mason kits which are ideal half-way house for those that can't decide between pre-make or DIY
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When it comes to solar battery storage, we understand that choosing the right storage solution for your solar energy is crucial, which is why we offer a range of options to suit your installation.
I have JBD (Overkill BMS). JK and Pace have had good reports from others on here, but I have yet to find anyone recommending Daly after more than 18 months on this forum.
Depending on your intended usage, I'd suggest a regular G98 or G99 type tested grid-tied hybrid (such as a Solis or Sunsync) and battery pack to suit.
As for fire risk, I'd be careful to design the system properly in the first place, whatever size. A small 100Ah sized system can still provide enough power to create too much heat.
When I built a system purely for grid outage backup I went with pre-loved SLA data centre backup batteries (Enersys SBS 190F). Four of those for a 48 V system to begin with, then added another four in parallel later. That gave us about 12 hours of comfortable backup capacity, longer if we were frugal.My curent set of batteries was adquired 12 years ago for an electric car conversion. Link
Data/telco centres cycle them out on a schedule and the batteries are designed exactly for this purpose. Can get them for not a lot of $, add a 4-5 kW AIO inverter and some relevant safety bits (fuse/breaker) to an AC distribution panel/outlet with suitable protection and you'll have a very nice power backup if using a generator is not your gig (not always suitable). Add a transfer switch and power inlet to the home and you'll be able to plug it in and cover the home's general power outlet and lights.
Leaving LiFePO4 fully charged all the time and rarely using them is not good for their health.
I'm generally not to found of sealed batteries with proprietary BMS controls. I'd rather use a high quality BMS or design my own and routinelly inspect and balance the cells and I guess most comercial options are really not designed for that. Anything with a warranty that it's worth the paper it's written on, will generally be prohibitivelly expensive and require a very restricted usage type, such as being coupled with their specific inverter. Once the warranty is gone, it's generally game over for any repairs that need doing.These echo my thoughts ^^^^, which is why I built my own battery pack. I like the control I have over the my system which I can tweak to suit my needs at any time I like.
Why do you think the 15KW battery pack will be more cost effective?If you are building your own, 300Ah cells are not 3x the price of 100Ah cells. And the fixed costs (DC wiring, fuses, isolators, BMS, case, bits for compression and inter-cell insulation) are almost identical if you are building a 15kWh pack, vs. a 5kWh pack. So the bigger one is more cost-effective.
I'm still apreensive on having such large batteries indoorI wouldn't do that - not worth the risk, IMHO. I'm probably over-cautious, but I'm old and still here Mine are in a garage 30m from my house.
What kind of prices are people here in the forum getting for 100A+ cells? I'm assuming import from china, right?I bought mine from Fogstar - EVE 304Ah cells are now only £81 each. You then don't have to worry about shipping, import duties and the worry they may not arrive. Again YMMV, but for me the cost-saving of direct import didn't exceed the hassle factor. Fogstar no longer do 100Ah batteries, but their 230Ah ones are only £40 each. So, you could buy those and only half fill them to get your 100Ah quota
I looked into car batteries, as they normally come with a nice enclosure,... if you have space on your drive then a little Prius or Leaf makes a nice enclosure for the cells! For you reading pleasure - the jury is still out on the cause other than we think the spark was an unsuitable type of fuse for the purpose. But the fuse that the vendor recommended.
If you are building your own, 300Ah cells are not 3x the price of 100Ah cells. And the fixed costs (DC wiring, fuses, isolators, BMS, case, bits for compression and inter-cell insulation) are almost identical if you are building a 15kWh pack, vs. a 5kWh pack. So the bigger one is more cost-effective.I can see why people are not using AliExpress. Still remember paying $15 + duties for my 10Ah's, so good to see the prices today are a fraction!
I wouldn't do that - not worth the risk, IMHO. I'm probably over-cautious, but I'm old and still here Mine are in a garage 30m from my house.
I bought mine from Fogstar - EVE 304Ah cells are now only £81 each. You then don't have to worry about shipping, import duties and the worry they may not arrive. Again YMMV, but for me the cost-saving of direct import didn't exceed the hassle factor. Fogstar no longer do 100Ah batteries, but their 230Ah ones are only £40 each. So, you could buy those and only half fill them to get your 100Ah quota
... if you have space on your drive then a little Prius or Leaf makes a nice enclosure for the cells!
For you reading pleasure - the jury is still out on the cause other than we think the spark was an unsuitable type of fuse for the purpose. But the fuse that the vendor recommended.
House burned down
So, after 4 to 5 years of working flawless, the 100 kwh lifepo4 battery caught fire at night and burned our house down. Luckily our family just made in out on time. Inspection of the fire expert revealed that a melt fuse melted, and created an arc between the 2 points wich ultimatly started the...
I know that I am going to line the walls and ceiling of any room containing batteries with firerock and/or durock. Firerock is gypsum board treated and thicker than regular sheetrock so it has a 4 hour burn time per thickness. Durock is cement board used under tile when you install it. One person has stated they are going to retrofit a sandwich of firerock-durock-firerock on walls and ceiling of their battery/electrical room.
In my case we are looking to buy property and build, so my utilities will be in a separate small building that is divided into a battery room and an electrical room.
Extreme ? yes. But if there is even a slim possibility of a fire that burns the house down I will not take chances.
I'm not a great appologist of lead acid batteries, considering their performance, but then I was never really able to find a good 'bargain' on them. They were expensive as far back as I can remember. Back in they early 's I did use second hand 6V Telecom batteries on a offgrid setup. I also used brand new 12V AGM's. The AGM's did a great job as starter batteries and performed relativelly well for UPS Backup, but that was it. Once one starts to cycle them, they degrade quicky, it's virtually impossible to charge them quickly and the voltage is nowhere as stable as lithium.
The battery backup is planned to stay in standby, mostly serving as a UPS for citical loads,That's a use case where there is bugger all cycling. Hence why suggesting batteries designed specifically for that use case. The batteries sit there at float ready to supply energy when you need it. There is no daily cycling.
I guess I messed up with that ALiExpress order, but let's see.
They will be slowly cycled depending on what available spare capacity I have, just not to a high discharge and charge rates as typically home storage batteries are used, where they are intended to supply the full household load as their primary function.
I have a smaller pack with 10Ah cells I use. That's been going strong for 10 years now, altough it is used to supply low voltage networking equipment / DVR / Alarm, that draws about 30W.
I figured out if I want to have the system running from the panels in case of grid failure, which does happen at times, particularly in winter with heavy snowfall, I might as well have a few KW available to run the gas boiler, circulation pumps, lights and anything else critical. Having the battery backup is the main aim and the grid injection is just a way to offset the cost of the batteries if and when I have spare capacity from the panels during the summer.
I have about 7KW of panels on an East / West configuration, producing roughly 5KW on the AC side. I’m exporting up to 16A (3.6-4KW) according to G98 limits and my battery charger is 1KW variable.
The battery backup is planned to stay in standby, mostly serving as a UPS for citical loads, though I will provision for the capacity to inject up to 500W into the grid to offset some consumption in the summer, after sun hours.
This is what's confusing about your posts. You talk about wanting "UPS" or outage back up:
That's a use case where there is bugger all cycling. Hence why suggesting batteries designed specifically for that use case. The batteries sit there at float ready to supply energy when you need it. There is no daily cycling.
Then you say you don't like them because you can't cycle them!
So what exactly is the scope of what you are looking to do?
Get that sorted first. Then design a system to deliver on your scope.
Solar energy storage systems are gaining serious traction as more homeowners and businesses prioritize energy independence and backup power during outages. With the 30% federal ITC now extended to both solar and standalone battery storage—and state-level incentives in places like California, Hawaii, Illinois, Maryland, Massachusetts, and Oregon—demand is only going up.
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Installers who understand the types of solar energy storage systems available, from AC- and DC-coupled setups to emerging hybrid inverters and long-duration battery tech, are in the best position to guide customers. Whether it’s sizing a residential solar power storage solution or integrating commercial-scale solar energy storage options, having a command of these technologies builds trust and adds value.
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Solar energy storage is essential for maximizing the value and reliability of solar power systems. Because solar energy is an intermittent source—only available during daylight hours—solar energy storage systems allow homes and businesses to store excess energy for use at night or during grid outages.
For off-grid systems, batteries are critical for providing 24/7 power availability. In grid-tied solar energy storage systems, hybrid setups with batteries enable homeowners to maintain power during blackouts and to shift energy usage based on cost and need.
In regions with time-of-use (TOU) electricity rates, solar energy storage solutions help customers reduce utility bills by storing energy when rates are low and discharging it when rates peak. This load-shifting capability can significantly reduce the solar system payback period while improving energy independence.
*Note: The "Cycle Life" values are approximate estimates
As the electrical grid ages and extreme weather events increase, power outages are becoming more frequent. In wildfire-prone regions, utilities are implementing planned Public Safety Power Shutoffs (PSPS) to reduce fire risk—leaving many homes and businesses without electricity for hours or even days.
While gas-powered backup generators offer a short-term fix, they rely on fossil fuels, generate noise, and emit carbon. In contrast, solar energy storage systems are a clean, quiet, and increasingly cost-effective solution. These systems store surplus solar electricity for later use—providing solar power backup during grid outages and helping stabilize the broader grid by balancing supply and demand.
In high-solar penetration regions, excess solar energy during midday often leads to curtailment or wasted electricity. This challenge is visualized by the duck curve, which illustrates the mismatch between solar generation and consumer demand. Solar energy storage helps address this by storing unused power during low-demand periods and discharging it when demand spikes—enhancing overall grid efficiency and reducing waste.
Installers should understand the different types of solar energy storage systems available—each suited to specific use cases based on application size, duration needs, and available space.
The most common form of solar energy storage today uses battery technology to store electricity. Popular battery chemistries include:
Lead-acid batteries (e.g., sealed AGM): Affordable but lower cycle life.
Lithium-ion batteries: High-efficiency and long lifespan. Two key chemistries:
Lithium Iron Phosphate (LFP) – Stable, long-lasting, and ideal for solar power storage.
Nickel Manganese Cobalt (NMC) – Higher energy density, common in compact systems.
These technologies dominate the residential and commercial solar energy storage market, offering flexible solar energy storage solutions for backup and peak shaving.
Less common but emerging, chemical energy storage stores power in molecular bonds rather than direct electricity. A key example is hydrogen energy storage, which uses electricity to produce hydrogen via electrolysis. The hydrogen can then be stored and used in fuel cells to generate electricity—suitable for long-duration solar energy storage options or remote/off-grid use cases.
These energy storage systems use a material, such as water, molten salts, or sand, in an insulated tank to store heat. Then, this energy is either used to generate electricity or is used to provide heat. Thermal storage is useful for concentrated solar thermal power (CSP) plants that focus sunlight to heat a fluid.
A relatively widespread application is solar thermal water heaters that use solar collectors to heat water in a storage tank. The hot water can then be used as domestic hot water or to heat buildings through a heat exchanger or a radiant floor heating system. However, researchers at Lawrence Berkeley National Laboratory are investigating how to take this to the next level using next-generation materials and systems.
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When it comes to solar energy storage systems, two main lithium-ion battery chemistries dominate the market: Lithium Iron Phosphate (LFP or LiFePO₄) and Nickel Manganese Cobalt (NMC). Both offer unique advantages, and understanding the differences is key when selecting the right solar energy storage solution for your clients.
NMC batteries are widely used for solar energy storage, and the Generac PWRcell, LG Chem RESU, Panasonic EverVolt, and Tesla Powerwall 2 are NMC batteries. However, the Enphase IQ, Fortress Power eVault, Sonnen Eco, and Tesla Powerwall 3 are LFP solar energy storage systems
LiFePO4 batteries offer several advantages for solar energy storage systems, combining safety, longevity, stability, and environmental benefits.
Safety: LiFePO4 batteries are known for their excellent safety profile. They are less prone to thermal runaway and are more stable at high temperatures than NMC solar energy storage batteries.
Long Cycle Life: LiFePO4 batteries typically have a longer cycle life compared to NMC solar energy storage systems. They can withstand more charge and discharge cycles before experiencing significant degradation.
Stability: LiFePO4 chemistry is inherently more stable, which contributes to a reduced risk of thermal runaway and enhances the overall safety of the solar storage system.
High-Temperature Performance: LiFePO4 batteries perform well in high-temperature environments, making them suitable for applications where elevated temperatures may be a concern.
Flat Discharge Curve: LiFePO4 batteries exhibit a relatively flat discharge curve, meaning they provide a consistent voltage output over a wide range of states of charge. This can be advantageous for certain applications.
Environmental Impact: LiFePO4 batteries are considered more environmentally friendly than NMC solar energy storage as they contain fewer rare and toxic materials.
NMC batteries provide several benefits to solar energy storage systems, particularly where space, weight, and cost efficiency are essential.
Energy Density: NMC batteries generally have a higher energy density than LiFePO4 batteries, meaning they can store more energy in a given volume or weight. This makes them suitable for applications where space or weight is a critical factor.
Cost: NMC solar energy storage batteries can be more cost-effective to manufacture, making them a popular choice for various applications where cost considerations are paramount.
Wider Voltage Range: NMC batteries often have a wider voltage range, providing flexibility in designing battery packs for specific voltage requirements.
Application Flexibility: Due to their higher energy density, NMC batteries are commonly used in electric vehicles and applications where maximizing energy storage in a limited space is crucial.
Typically, LFP solar energy storage systems have a longer lifespan and are safer. In contrast, NMC batteries are usually a bit less expensive, have a higher energy density, and can withstand colder temperatures slightly better. However, NMC solar energy storage systems are not necessarily more cost-effective than LFP batteries because they can have a shorter lifespan.
When selecting a solar energy storage system, it is also helpful to consider the inverter. Some solar energy storage batteries are AC coupled, so they have built-in battery inverters. Because AC-coupled solar systems do not require a hybrid inverter, they work with microinverters and string inverters.
If a DC-coupled solar energy battery is used, a hybrid inverter, such as the SolarEdge StorEdge, is required. AC-coupled batteries include models like the Enphase IQ, Generac PWRcell, Sonnen Eco, and Tesla Powerwall 2.
Choosing the right solar energy storage system is essential for a successful project. While many options are available, some are better suited for specific applications or configurations. Understanding your project’s goals and budget is key to selecting the best solar energy storage solution. The GreenLancer team is here to assist with all types of solar energy systems.
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